I am going to fly novice and sportsman SMA pattern, these are pre 75, 60 size pattern planes, both motors are legal but which would perform better Os61 FX or Saito 91 S, planes I have at this time are the AVENGER and the Intruder, also I'm concerned about maintenance on 4 cycles is there more, also vibration is this a problem. Any imput would be deeply appreciated!!!!!!!

Thank You

if you are speaking of the SPA. The motor of choice in our group seems to be the OS 91 FS. Very reliable. Its in about 90-95% of the SPA aircraft at a meet. I am installing one in an ALtair for SPA.
Also have one in a Daddy Rabbit that I compete with now.
The Altair is a huge plane as far as SPA planes go, it will be weighing in at about 7.5 lbs i think. Check it out at my webpage . The webpage is fairly new, and lacks much content. But the Plane constuction of the King Altair is full of photos. and some good photos of the Huntsville contest, we took photos of all the contestants .

gwair.com

BTW:
My OS 91 has about 60 flights on it, and i have only adjusted the needle valve so far. They are great engines, and serve well in an SPA aircraft.